This project seeks to determine the location and mechanism of transmitter secretion and reception at synapses. In order to capture the fleeting structural changes which accompany discharge of synaptic vesicles, methods for rapidly freezing synapses have been developed. Structural changes are then visualized at the cell membrane level by preparing the frozen tissues with freeze-fracture technique. The freeze-fracture technique also reveals structural details which may be specific for different pharmacological types of synapses; this relationship is being investigated by examining the structure of the post-synaptic membrane in different types of synapses. New methods are also being tried for marking specific chemical activities, such as receptors, to identify them in freeze-fracture, as well as conventional thin section preparations. The assembly of viral membranes is being used as a simple model with which to develop these techniques. The significance of this work is that it defines the normal structure of synapses and relates normal variations in structure to different functional states. Thus, it becomes possible to distinguish pathological changes in structure, which is an issue of great importance in looking for the etiology of epilepsy or myesthenia gravis with structural techniques.